Thin hot rolled steel strip is generally produced by reducing the thickness of cast slabs in successive rolling steps until the desired thickness is reached. At the end of the rolling mill there is normally a coiler which winds up the strip into a coil for its handling.
The coiler comprises several supporting rolls and at least a pair of pinch rolls which drive the strip at the desired velocity and tension before it is engaged by and wound up on a coiler mandrel.
The pinch rollers are usually located at a higher position with respect to the coiler roll and a set of guiding plates forces the strip towards the coiler mandrel. The prior art coilers include a pivoted movable flap guide which can switch its position so that it diverts the strip head end towards one of a plurality of coiler mandrels in those mills comprising several coiling mandrels for higher productivity of the rolling mill.
The flap guide of the prior art leaves a gap of a minimum of 1 to 2 mm between the guide end and the upper pinch roll, chosen according to the expected strip thickness. Any smaller gap has not been thought practical due to normal play and tolerance variables. When the thickness of the strip is more than about 2.0 mm to 1.5 mm, generally no problems are found in handling the strip, but when the thickness is less than about 1.5 mm then the strip may pass through said gap and get wound up around the pinch roll, causing delays and generating scrap. The thinner the strip, the more flexibility, and the higher the resulting velocity (typically above 10 m/s for a 1.5 mm thickness or less). The high speed of the strip causes its head end traveling through the cooling section of the mill sometimes to lift upwardly and when the curvature of head end is about the same of the pinch roll, it is very likely that the strip will become wound up in said pinch roll. Therefore, the invention is particularly useful in coiling systems where thin steel strip is produced.
Although several proposals addressed to maintaining the head end of the strip within the normal path were considered and tried, the solution to this problem was finally discovered by the applicants when the conventional flap guide was redesigned and operated so that it makes brief non-abrasive actual close contact with the upper pinch roll as the strip head end passes the roll, actually eliminating the gap (thought previously in the prior art to be a necessary requirement). In order to avoid undesired relatively rapid wear and marking on the pinch roll surface, which in turn would affect the quality of the strip, the tip of the flap guide in contact with the pinch roll is made of a material having a very low friction coefficient. One of the preferred materials for this application is a composite fiber reinforced material known as "Micarta" (trademark of Westinghouse Electric Corporation) which finds many applications as a hard non-abrasive machinable material, but some other material may be used as long as it does not cause any significant wear or mark on the pinch rolls.
The following patents were found in a search made in connection with the present invention: U.S. Pat. No. 2,920,838 to Priestley; U.S. Pat. No. 4,047,416 to Johnson; U.S. Pat. No. 4,761,983 to Ginzburg et al. and U.S. Pat. No. 5,479,807 to Moser; the contents of which are incorporated herein by reference.
Priestley discloses a strip coiling apparatus for coiling continuous strip of a relatively heavy gauge, and is addressed to prevent objectionable markings of the strip caused by the pressure set up when the coiler rolls strike the strip at the overlap or point of increased coil diameter, and is also directed to providing curved guides and fluid jets which impinge upon the leading edge thus to cause the strip as it enters the coiler to be bent toward and forced against a peripheral surface of a rotating reel. This patent does not teach or suggest the solution provided by the present invention to prevent the winding problems encountered with thin gauge strip.
Johnson discloses an apparatus for uncoiling and straightening strip material of considerable thickness and for directing the leading edge of the uncoiled material to a straightening and feeding mechanism. This patent however does not disclose the problem of thin strip winding solved by the present invention.
Ginzburg et al. describes a method and apparatus for winding material onto a coiler drum along a passline of a hot reversing mill. The apparatus comprises an apron 34 pivotally moved by a hydraulic cylinder but is not used for preventing the strip material from winding on pinch rollers.
Moser discloses a coiler furnace for a hot strip comprising a strip-receiving guide having an end adjacent to the coiler drum when in a strip receiving position. This guide however is not intended to prevent the strip from winding on pinch rolls or to contact said rolls.
None of the above mentioned patents teach or suggest the problems solved by the present invention nor teach the construction and operation of a guide as claimed in the present invention.